Known electric machines comprises a stator, and a rotor which rotates about an axis with respect to the stator.
In these known electric machines, the stator comprises an outer cylinder, and stator segments arranged about the axis. The rotor comprises an inner cylinder, and rotor segments arranged about the axis; and each rotor segment comprises modules made of magnetizable material and arranged, parallel to the axis, inside the rotor segment.
To activate such known electric machines, the modules of magnetizable material must be magnetized (i.e., a material or object that produces a magnetic field). More specifically, each module of magnetizable material is made of material that can be magnetized to produce a magnetic field. This is done by adopting an electric machine activating method, which comprises a module magnetizing step, after and by virtue of which each module produces a magnetic field and is known as a magnetized module.
The magnetizing step is performed by a magnetizing device, which magnetizes the modules of magnetizable material with magnetizing flux of a given strength.
The strength of the magnetic field produced by each module changes, in particular gets weaker, over the working life of the module, so that, after a certain time period, normally ranging between ten and twenty years, each module is no longer capable of producing a magnetic field capable of effectively interacting with the magnetic field produced by the stator, with the result that the machine is no longer active, and must therefore be reactivated by remagnetizing the modules. This involves further magnetization of the previously magnetized modules, which, once remagnetized, define magnetized modules in all respects.
Such known electric machines are typically activated by: magnetizing each module; fitting each magnetized module to the inner cylinder of the rotor; fitting the stator segments to the stator; and connecting the rotor, with the magnetized modules, to the stator with one or more bearings.
However, this known method poses the technical problem of having to handle each magnetized module, which is a dangerous job on account of the module generating strong forces which interact with other modules or ferromagnetic parts. That is, when fitting each magnetized module to the rotor, the magnetized modules already fitted to the rotor interact with the one being assembled. For this reason, the magnetized modules must be assembled using special tools and in premises designed for the job. More specifically, in the case of an electric machine that has never been operated, the magnetizing step is performed at the factory; whereas, if the electric machine forms part of a system and needs reactivating, it must be dismantled from the system and sent to the factory, and each module or group of modules must be removed, and each group of modules remagnetized. This is obviously a long, painstaking procedure involving numerous man-hours and considerable cost, and which also calls for transporting an electric machine with the rotor magnetized.